Well, this seems to be a common problem that’s sparsely answered. Windows Live Mail suddenly lost the ability to send new messages through my Hotmail account.
I can check emails, I can sort them and even get new feeds, but can’t send emails no matter what. This turned out to be part of a two pronged assault on my sanity by both my AV software and Comcast. It turns out that I can only send email on 587 on Comcast and Avast was having an issue with my outgoing mail scan.
Go to Tools > Accounts and select your mail account. Click on Properties to bring up the following window and go to the “Advanced” tab.
Then you need to tweak your anti-virus client. I use Avast, but the procedure should be the same for other AV clients.
Just make sure you leave inbound scanning alone since it’s pretty stupid to have an AV suite that doesn’t check emails.